Vacuum-electric switches have been widely used for controlling the various functions of automotive heating, air conditioning and ventilating systems. Virtually all such systems include a fan or blower for circulating air into the cab of a vehicle. The fan is driven by an electrical motor which is energized and de-energized by the electrical switching components of the vacuum-electric switch. If the vehicle is equipped with air conditioning, the vehicle is provided with an air conditioning compressor which is typically driven by an electrically operable clutch connected between a drive pulley and the air conditioning compressor. A belt extends between the drive pulley and another pulley which is rotated by the engine of the vehicle. The energization of the air conditioning clutch is controlled by additional electrical switching components of the vacuum-electric switch.
The system is typically provided with a variety of dampers or doors whereby the intake and outflow of air to and from the blower may be controlled. Typically, the dampers or doors are adapted to be moved by vacuum operable motors or devices. The supply of vacuum to the vacuum motors is controlled by the vacuum switching components of the vacuum-electric switch.
The general concept of a rotary vacuum-electric switch is disclosed by the Raab and Cobb U.S. Pat. No. 4,679,588, issued Jul. 14, 1987 and assigned to the assignee of the present application. The switch of such patent comprises a rotatable operating shaft connected to a pinion gear which meshes with a linear gear rack on a translatable valve carriage. A silicone rubber valve is movable with the carriage and is adapted to control the supply of vacuum to a variety of ports, adapted to be connected to the various vacuum motors. An electrically insulating switch carriage is rotatable with the shaft and is provided with two electrically conductive contactors which are movable with the electrical carriage along arcuate paths. The contactors are adapted to engage stationary contacts for controlling the energization of the fan motor and the air conditioning clutch. The electrically insulating carriage has an arcuate detent portion formed with a series of detent notches adapted to be engaged by a spring-pressed detent ball.
While the rotary vacuum-electric switch of the above-mentioned patent is functional and operative, it leaves a great deal of room for improvement, particularly as to adaptability to a wide range of applications, compactness and ease of assembly. Another rotary vacuum-electric switch is disclosed in the present applicant's co-pending application, Ser. No. 07/697,592, filed May 8, 1991 and assigned to the assignee of the present application. Here again the switch comprises a rotatable operating shaft which carries a pinion gear meshing with a linear gear rack on a translatable vacuum valve carriage. The switch also comprises a translatable electrical carriage operable in response to rotation of the shaft by a complex gear drive. Fan and clutch switch contactors are mounted on the electrical carriage. The complex gear drive has a tendency to introduce a significant amount of hysteresis into the driving relation between the rotary shaft and the translatable electrical carriage.